Muscle growth and composition in heavy and light breed chickens adapted to intermittent feeding

1. The effect of intermittent feeding in chickens of heavy breed (HB; meat type) and light breed (LB; egg type) on skeletal muscle growth and composition was studied in adapted and non-adapted chickens. 2. Food intake, relative to body-weight, was similar in both breeds but was higher in ad lib.-fed than in intermittently fed birds. 3. On repletion days the relative growth rate was similar in both breeds, while on depletion the LB chickens lost more weight than the HB chickens. In both breeds, the relative growth was higher in the intermittently fed birds during days of food restoration than in those fed ad lib. 4. The relative weight of the breast muscle was higher in HB birds than in LB birds, but deposition rate on the day of food restoration was similar in both breeds. This growth was more pronounced in chickens adapted to alternate feeding than in chickens exposed to this feeding regimen for one cycle. 5. Protein concentration in breast muscle was not affected by age and was slightly higher in LB chickens than in HB chickens. Soluble protein was markedly reduced on days of repletion, and more at 46 d than at 18 d of age. 6. The RNA:DNA ratio was higher in HB than in LB chickens, and lower on days of food deprivation than on days of food restoration. After repletion this ratio returned to the level of the ad lib.-fed chickens. While in LB chickens cell size (as estimated by DNA concentration) remained constant on repletion and depletion days, in the HB chickens it decreased. 7. The rapid growth of breast muscle in HB chickens was attributed to the higher rate of protein synthesis (estimated by RNA:DNA ratio) compared with LB chickens. This may also explain why the breast muscle of LB chickens was less sensitive to intermittent feeding than that of HB chickens.